Thermionic cathodes (also referred to as hot cathodes) are cathode electrodes which emit electrons when heated, due to thermionic emission. They are a standard component in many vacuum electronic devices, including those requiring high reliability and a proven legacy, as many customers and targeted applications are attracted to thermionic technology due to the decades of testing these devices have undergone. For example, thermionic cathodes may be used in high power microwave devices, compact electron accelerators, amplifier tubes, klystrons, and medical x-ray imaging machines. The temperature for thermionic emission may be as high as about 1000° C. or greater.
In order to improve thermionic emission efficiency, a finite amount of barium oxide (BaO) is added to the thermionic cathode to activate the thermionic cathode. BaO has been demonstrated to improve the probability of emission when heated to a high temperature (e.g., about 1000° C.). However, at high temperature, BaO is also driven off into the vacuum space enclosing the thermionic cathode. As such, BaO may be lost to the vacuum space and therefore the effect it has on the probability of emission is also diminished.